Question

Assume we have the following data in a SQL Server table (sorted by name) :

Id   Name        LName
-------------------------
5   Abbas        Dayyan
3   Mohammad     KD
4   Nima         Ahmad
1   Omid         Zangene
2   Pedram       Ahmadi

we have an Id query string and we wanna get the next and previous row (if exists) from Id.

e.g :

the Id query string is 4, so we wanna get Mohammad KD as previous row and Omid Zangene as next row.

Could you please guide me how can do it with LINQ to Entity Framework.

Edit:
In practice the number of table rows is around 1 million.
Table rows didn’t sort by Name by default, wa need to sort them by Name for the result.

Answer 1

How about this?

var result = (from person in db.People
              where person.Id == id
              let ordered = db.People.OrderBy(p => p.Name)                  
              let reversed = db.People.OrderByDescending(p => p.Name)                  
              let previous = reversed.SkipWhile(p => p.Id != id).Skip(1).FirstOrDefault()
              let next = ordered.SkipWhile(p => p.Id != id).Skip(1).FirstOrDefault()
              select new { previous, next }).First();

Edit: Took the new specifications into account.

Edit 2: Modified the code to not use LastOrDefault, which doesn’t work with LINQ to Entities.